How to properly pass selected value by ajax request to php file?

Question

1C-Bitrix

Hello!

I can’t figure it out, there is a select with several option values, each option has an id with a unique value.
When choosing a certain option, using ajax request, I send this value to the template of the sale.order.ajax component, but when displaying it in this template, or checking if this variable exists, nothing happens, here is the code:
jQuery

$("#cart-part_region").change(function(){

      if($("#cart-part_region option:selected").val() !== '0'){
        
        let id = $("#cart-part_region option:selected").val();

        $.post('/local/templates/eshop_bootstrap_v4/components/bitrix/sale.order.ajax/bootstrap_v4/template.php', {id: id}, function(data) {
          $('.cart-part_city').show();
          alert(id);
        });

Here is the code in the template.php file

echo ($_POST['id']);
?>
      <div class="cart-part_city">
        <div class="cart-part_form-name mb-3">
          <span>Город:</span>
        </div>
        <div>
          <select id="cart-part_city">
            <option selected value=0"">-</option>
          </select>
        </div>
      </div>

I don’t understand why it’s impossible to accept this variable, either I’m doing something with Bitrix, or I’m doing something wrong.
Or somehow, when selecting select, you can get the id and put it in CIBlockSection::GetList().
Thanks in advance!

Answer 1

<option selected value=0"">